The invention relates to a device for separating metal parts from a stream of material to be conveyed, the device comprising a metal detector and a multiple-way junction controlled by the metal detector, the multiple-way junction comprising an inlet and two selectively controllable outlets.
In U.S. Pat. No. 5,377,847 a device for separating metal parts from a stream of material to be conveyed is described, where the multiple-way junction comprises a damper which can be swivelled about a transverse axis by a solenoid. In the end position the damper guides the stream of material to be conveyed to a first outlet opening which can be designated as material opening. In the opposite end position of the damper the stream of material to be conveyed is fed to a second outlet opening which can be designated as separation opening. The multiple-way junction is controlled as a function of the signals from a metal detector such that a stream of material to be conveyed, which does not contain any metal parts, is fed to the material opening while the damper is reversed when a metal part is detected. Thus the metal part and part of the stream of material to be conveyed are fed to the separation opening. When the conveying device is at a standstill or at a low velocity of the stream of material to be conveyed it may happen that the damper is blocked by the weight of the material to be conveyed. When the stream of material to be conveyed is moved with the aid of an air flow, problems with regard to tightness play an important role. It is difficult to ensure that the multiple-way junction remains tight in each damper position such that no air is taken in from outside and no compressed air leaves the conveying track. Solving this tightness problem requires high sealing efforts.
A device for separating metal parts described in DE 39 31 579 C1 comprises a multiple-way junction having a horizontally movable funnel-shaped slide which is open at its upper side. Here, sealing the conveying track beyond the multiple-way junction is not intended.
For tube conveyors multiple-way junctions are known which selectively feed the stream of material to be conveyed from an inlet to one of a plurality of outlets. Such a rotary tubular multiple-way junction according to U.S. Pat. No. 5,269,638 comprises a rotary element in a housing having an inlet opening and two outlet openings, the rotary element being of single-duct or dual-duct configuration. In the case of a single-duct rotary element the duct is connected with either of the outlets when the rotary element is rotated while it is permanently connected with the single inlet. In the case of a dual-duct rotary element the two ducts are completely separated from each other so that can have only very small passage cross-sections. In any case, such a rotary tubular multiple-way junction would not be suitable for metal separators since a rotation of the rotary element by 180xc2x0 is necessary. What is desired is a relatively small rotation which allows a short response time. In the case of a single-duct multiple-way junction a rotation of the rotary element by at least 90xc2x0 is necessary and in the case of a dual-duct multiple-way junction a detected metal part may not enter the duct for the metal-free stream of material since otherwise separation is not possible.
It is an object of the present invention to provide a device for separating metal parts, which can be configured with small dimensions and has a short change-over time.
The device according to the invention is configured as rotary tubular multiple-way junction having a tubular housing. An inlet opening and two outlet openings are arranged on the circumference of the housing. The housing contains a rotary element which selectively connects the inlet opening with either of the outlet openings. The rotary element comprises two adjacent inlet ducts extending at an acute angle to each other, and an outlet duct connected with both inlet ducts. By rotating the rotary element by less than 90xc2x0 it is possible to change over between passage and separation. The change-over angle is preferably smaller than 90xc2x0 and amounts to 30xc2x0 to 60xc2x0. Thus the rotary element is allowed to have a relatively small diameter and relatively wide ducts. The duct volume of the rotary element is small so that, apart form the metal parts to be separated, only a small amount of material is separated. Further, short response times are realized.
The device is adapted to be directly mounted to the supply opening of a processing machine since it has smaller dimensions and a short response time. The device needs only little space and has an extremely small mounting length.
According to a preferred embodiment of the present invention the inlet ducts join each other without a partition being provided. This means that the inlet ducts are permanently congruent with the inlet opening of the housing so that the inlet opening is never closed or reduced in size during operation of the device. Of course, it is possible to set the rotary element in such a position that the inlet opening is closed, e.g. when the conveying device comes to a standstill.
The inlet opening and one outlet opening are preferably arranged diametrally opposite each other and the second outlet opening is offset relative to the first one by less than 60xc2x0. In this case, under normal conditions the stream of material to be conveyed moves diametrally along the rotary element without being diverted. When the metal detector responds, the rotary element is rotated by less than 60xc2x0 so that the stream of material to be conveyed is diverted at an acute angle which is even smaller than 60xc2x0.
The width of the inlet ducts and the outlet duct preferably amounts to 0.4-times the diameter of the rotary element. Thus the volume of the rotary element is utilized to a large extent for material conveyance purposes.